This article is pending and will talk about coprocesses used in shells.

A coprocess is a process run asynchronously on a shell that has a pipe for stdin, stderr, stdout, etc. attached to the main process. By this way you are able for example to redirect a main process output both to a log and to stdout at the same time.

http://www.gnu.org/software/bash/manual/html_node/Coprocesses.html

http://www.linuxjournal.com/content/bash-co-processes

http://www.gnu.org/software/bash/manual/html_node/Redirections.html#Redirections

http://www.dartmouth.edu/~rc/classes/ksh/coprocesses.html

 http://wiki.bash-hackers.org/syntax/keywords/coproc